Technically, wasn't there an exchange? The OGL granted certain rights, while imposing certain requirements? That's more of a transaction than a sharing.
WotC's interaction with the OGL is a little bit different from everyone else's.
One way to think about it is that there are two chains of ownership. One is D&D, the other is the SRD. They are not the same.
WOtC has D&D. Lock, stock, and barrel. 3e, 4e, 5e, etc. WotC is under no OGL requirements regarding D&D because they own it.
WotC also put out the SRD under the OGL.
The SRD is derived from D&D, but is not D&D. If you're using material from the SRD, basically you shouldn't ever look at a D&D book.
The OGL allows other people to use material from the SRD, but they must accredit the source (in Section 15), include the OGL, and anything derived from OGC must also be OGC (so if you invent a new game mechanic, it's not required to be OGC. Hero point systems were often not declared OGC.)
The OGL does not require you to give up copyright (indeed, you have to have copyright to agree to the license); it's a license that lets other people use your copyrighted material so long as they do so under the same license you did (the OGL).
If WotC wanted to use someone else's OGC, they would have to use the OGL, or reach an independent agreement with the copyright holders.
Since WotC essentially* never used anyone else's OGC, they really just shared outward/downstream.
I suppose normal OGL use could be considered a transaction; I think of sharing as a two-way street (otherwise it's just giving) in which both parties voluntarily give the other something. The upstream OGL user is sharing blindly downstream - they have no idea who will reuse their material. I guess that's what differentiates it from a transaction in my mind.
Anyways, it's all minor nitpick stuff and I'll shut up about it.
*I know there were two monsters in the FF or MM2 or something, and maybe a little bit here and there, but overall? Nothing.
Edit: OK, so my original point in response to the original post about WotC not giving away ALL of their intellectual property: WotC still owns all of their intellectual property. They do not control the reproduction of the game mechanics that were released under the OGL so long as they are reproduced under the OGL, but WotC still owns the property. It's not in the public realm.